1. Field of the Invention
The present invention relates generally to methods of insulating buildings and creating an air current that may be used to generate electricity. More specifically, the present invention includes a process and system for insulating buildings against heat transfer, including conduction, convection and radiation heat transfer, and thereby creating an air flow between the soffits and a roof vent, which may be used to spin turbines that create electricity.
2. Description of the Prior Art
There are many systems and products currently available for insulating buildings and homes. Proper insulation reduces energy costs. A well insulated structure does not gain or lose heat as quickly as a poorly insulated one, so it is easier to maintain a comfortable temperature within the structure. The retention of conditioned air lowers the demand on the heating and cooling systems, which reduces operating costs and extends the life of the system.
Available in a variety of forms, home insulation can be purchased in blankets, in batts, in a form which is bagged and ready to pour, and in a form which must be blown in place by a contractor using specially designed equipment. Three basic types of products are most commonly used. They include:
1) mineral wool, which includes rock wool and fibrous glass. Both of these products can be blown in place, or purchased in blankets or batts with a foil or paper vapor barrier. Rock wool can also be purchased in bagged form.
2) Plastic foam/resin, which is made of polystyrene, polyurethane, or urea formaldehyde, can be purchased in pre-formed sheets or bolts, or foamed in place by a contractor. Foam insulation can vary considerably in its final properties depending on the operator's skill, how various reactants are mixed, and the time allowed for curing.
3) Cellulosic insulation, made of any finely ground cellulose product such as recycled newspaper, can be poured or blown in place.
One problem associated with these types of insulation systems is that none of them provide insulation against all three main types of heat transfer: conduction, convection and radiation. For that reason, another type of insulation product has been made available on the insulation market. This product consists of one or two layers of bubble material laminated between layers of aluminum foil to provide thermal resistance. The bubble material is similar to the commonly available bubble-wrap packing material, which is essentially a plastic sheet containing a pattern of enclosed air bubbles.
Conduction is the transfer of thermal energy from a region of higher temperature to a region of lower temperature through direct molecular communication within a medium or between mediums in direct physical contact without a flow of the material medium. The transfer of energy could be primarily by elastic impact as in fluids or by free electron diffusion as predominant in metals or phonon vibration as predominant in insulators. In other words, heat is transferred by conduction when adjacent atoms vibrate against one another, or as electrons move from atom to atom. Conduction is greater in solids, where atoms are in constant contact. In liquids (except liquid metals) and gases, the molecules are usually further apart, giving a lower chance of molecules colliding and passing on thermal energy.
Heat conduction is directly analogous to diffusion of particles into a fluid, in the situation where there are no fluid currents. This type of heat diffusion differs from mass diffusion in behavior, only in as much as it can occur in solids, whereas mass diffusion is limited to fluids. Metals (eg. copper) are usually the best conductors of thermal energy. This is due to the way that metals are chemically bonded: metallic bonds (as opposed to covalent or ionic bonds) have free-moving electrons and form a crystalline structure, greatly aiding in the transfer of thermal energy.
As density decreases so does conduction. Therefore, fluids (and especially gases) are less conductive. This is due to the large distance between atoms in a gas: fewer collisions between atoms means less conduction. Conductivity of gases increases with temperature but only slightly with pressure near and above atmospheric. Conduction does not occur at all in a perfect vacuum. Conduction always takes place from higher to lower temperature.
Convection is a combination of conduction and the transfer of thermal energy by fluid circulation or movement of the hot particles in bulk to cooler areas in a material medium. Unlike the case of pure conduction, now currents in fluids are additionally involved in convection. This movement occurs into a fluid or within a fluid, and cannot happen in solids. In solids, molecules keep their relative position to such an extent that bulk movement or flow is prohibited, and therefore convection does not occur. Convection occurs in two forms: natural and forced convection.
In natural convection, fluid surrounding a heat source receives heat, becomes less dense and rises. The surrounding, cooler fluid then moves to replace it. This cooler fluid is then heated and the process continues, forming a convection current. The driving force for natural convection is buoyancy, a result of differences in fluid density when gravity or any type of acceleration is present in the system. Forced convection, by contrast, occurs when pumps, fans or other means are used to propel the fluid and create an artificially induced convection current. Forced heat convection is sometimes referred to as heat advection, or sometimes simply advection. But advection is a more general process, and in heat advection, the substance being “advected” in the fluid field is simply heat (rather than mass, which is the other natural component in such situations, as mass transfer and heat transfer share generally the same equations). In some heat transfer systems for buildings, both natural and forced convection contribute significantly to the rate of heat transfer.
Radiation is the transfer of heat through electromagnetic radiation. Hot or cold, all objects radiate energy at a rate equal to their emissivity times the rate at which energy would radiate from them if they were a black body. No medium is necessary for radiation to occur; radiation works even in and through a perfect vacuum. The energy from the Sun travels through the vacuum of space before warming the earth.
All three types of heat transfer discussed herein are applicable to home and building insulation, and it is desirable to insulate against each of these types of heat transfer in order to obtain maximum efficiency of the insulation system.